Objective:

In order to understand the effects of macroalgal blooms on nutrient retention within shallow coastal systems, the objectives of my research are:

To quantify the effects of macroalgae on water and sediment chemistry, focusing in particular on changes in the quantity and quality of sediment OM.

To determine the short-term fate of macroalgal organic matter within the water column and sediments during bloom and senescent periods across multiple nutrient loading rates

To quantify the uptake of carbon and nitrogen by macro- and microalgae across multiple nutrient loading rates and assess competition between autotrophs.

Approach:

To trace the uptake and fate of macroalgal organic matter within a shallow coastal lagoon, my approach combines the use of lipid biomarkers, 13C and 15N labeling, and compound specific isotope analysis of microbial biomarkers both in field and laboratory (mesocosm) studies. Because macroalgal biomass within a lagoon is hypothesized to be closely associated with the lagoon’s degree of eutrophication, my research will contrast a pristine with an impacted coastal lagoon along the Delmarva Peninsula. The field monitoring will be used to contrast the effects of different nutrient loading rates and varied macroalgal abundances on water quality and sediment chemistry. However, with the monitoring efforts alone, the separate pathways of carbon and nitrogen and the causal mechanisms determining those pathways cannot be deduced. Two mesocosm experiments will be conducted to explicitly determine the short-term fate pathways of macroalgal carbon and nitrogen using isotopically labeled macroalgae. A third mesocosm experiment will follow the uptake of carbon and nitrogen by macroalgae in the presence of additional primary producers (phytoplankton, benthic microalgae).

Expected Results:

Shifts in land use resulting from population increases and associated development along the coasts have and will continue to accelerate delivery of nutrients to coastal bays. I predict that this will result in a continued shift towards macroalgal dominated systems, and as a result, nutrient cycles will be changed significantly. I expect that my research will demonstrate that macroalgaes act only as a temporary sink for incoming nutrients and effectively diminish the role of coastal lagoons as nutrient filters. With increasing nutrient loads, the macroalgal bloom and die-off will result in a positive feedback cycle resulting in increased nutrient cycling rates: the re-release of inorganic nutrients to the water column will fuel additional algal blooms, which will again die off, releasing additional nutrients to the water. This will result in expanded areas of hypoxia and anoxia and negative impacts on fisheries, aquaculture, and recreational activities.

Progress and Final Reports:

The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.